This invention relates to a new metallic tone powder coating composition of acrylic resin series which provides a coating film having excellent weather-resistance and beautiful appearance and is suited for use in electrostatic powder spraying.
Solvent-containing paints have widely been used heretofore for coating metal or other kinds of materials. With a view of avoiding air pollution caused by solvents in the paints, however, a variety of powder paints are being developed recently.
Among various powder paints, acrylic powder paints are excellent in weather-resistance and hence are suitable for coating cars and electric instruments. In such applications, a fine coating appearance having a metallic tone is frequently required.
In order to obtain a paint film having a metallic appearance, a metallic tone paint is prepared and used in which a powder of such metal as aluminum, brass or bronze has been suspended, even in the case of a powder paint, into a solution of a resin. In the case of such powder paint where no solvent is present, the surface of the metal powder is not coated with a resin by merely blending the metal powder with the resin powder. When such metallic tone paints were applied according to the electrostatic coating method which is the most convenient for practical application of powder paints, it was found extremely difficult to perform the coating operation practically for the reason that the metal powder and the resin powder are quite different in electrostatic characteristics. In addition, there is a high possibility of dust explosion due to static electricity and the metal powder may be oxidized by the action of a high electric voltage employed during the electrostatic coating operation, whereby the metallic tone may also be changed.
On the other hand, a metallic tone powder paint produced by mixing a metal powder with a resin in molten state to coat the surface of the metal powder with the resin and thereafter, finely pulverizing the mixture after cooling has drawbacks in that it fails to provide a paint film with a desired metallic tone appearance as the form and structure of the metal powder are altered during the pulverizing operation and that there is a great possibility of dust explosion in the course of the pulverizing operation.
As the result of much research carried out for the purpose of developing a metallic tone powder coating composition of acrylic series which is improved in the above-mentioned problems seen in the conventional metallic tone powder paints, it has now been found that such purpose can be attained and the afore-mentioned drawbacks can be overcome by a composition comprised of a specific copolymer and a polymer-capsulated metal powder composite material prepared by chemically combining the metal powder with a synthetic resin according to a specific treatment. This invention has been accomplished on the basis of the above finding.